In an integrally geared centrifugal compressor, pressurized gas tends to leak axially along the rotating shaft of the compressor and into the driving mechanism such as an oil lubricated gear box. Cartridge seals provide safe operation of the compressor by properly sealing, venting, or buffering the pressurized gas from the oil lubricated gear box. In compressors for compressing gas such as oxygen, oil used for lubricating the gear box must be isolated from the oxygen to prevent fires.
FIG. 1 illustrates a prior art cartridge seal 10 which comprises a bronze shell 12 having a single, elongated, silver sleeve 14 disposed therein. Sleeve 14 is provided with a plurality of ports extending through both shell 12 and sleeve 14 and opening onto the inner surface of sleeve 14 for venting or providing a buffering gas between sleeve 14 and a shaft of a compressor (not shown). During manufacture, a semi-finished silver sleeve 14 is installed into a semi-finished shell 12 and the various ports are drilled through shell 12 and sleeve 14 while assembled together to ensure proper alignment. The inner bore is finished to its required diameter ensuring proper concentricity with the outer diameter of the cartridge. The cartridge seal is then disassembled, deburred, and cleaned prior to final installation into a compressor.
The illustrated prior art cartridge seal 10 while suitable for its intended purpose includes a number of drawbacks. The fabrication of cartridge seal 10 is labor and time intensive due to the required drilling and deburring of the ports. In addition, increasing the number of ports to increase the flow areas between the shaft of the compressor and sleeve for venting or providing a buffering gas reduces the strength of the sleeve and/or shell.
U.S. Pat. No. 4,343,591 to Hannan, III et al. discloses a turbomachine seal system having first and second seal members spaced axially about the shaft of the turbomachine to define therebetween a first annular chamber. Shims are required for positioning the seals axially and radially about the shaft.
U.S. Pat. No. 4,500,096 to Tuttle et al. discloses a turbine shaft seal assembly having three split seals with axial portions or dowel pins which abut each other or which require spacer rings to axially position the seals relative to each other. A gland exhaust opening is provided in the turbine case between the first and second split rings, and a gland exhaust opening is provided in the turbine case between the second split seal and the third split seal.
A drawback of the above disclosed seal assemblies having multiple seals is that they require separately configured elements for positioning the seals axially and/or radially about the shaft of the turbine. In addition, the seal elements are typically fabricated entirely from materials best suited to the gases, e.g., expensive metals or metal alloys. Furthermore, the seal elements typically require excess material in order to properly position the seal which also increases the overall cost.
Therefore, there is a need for labyrinth cartridge seals comprising a shell and a plurality of sleeves using a minimum amount of sealing material and having corresponding portions to prevent axial and radial movement therebetween, which reduce the labor, time, material, and/or cost required for fabrication, and which provide increased areas for venting or receiving a buffering gas to isolate a gas being compressed from the drive mechanism of the compressor.